Pickup for musical instruments



Oct. 27, 1964 c, EVANS 3,154,701

PICKUP FOR MUSICAL INSTRUMENTS Filed May 28, 1962 INVENTOR cm u/vcsrRICHARD El /1N8 Evan, Dam Elli/ cf United States Patent 3,154,701 PICKUPFOR MUSICAL INSTRUMENTS Chauncey Richard Evans, Kalamazoo, Mich,assignor to AftuIlJg (lilorporation, Salt Lake City, Utah, a corporation0 ta Filed May 28, 1962, Ser. No. 197,963 4 Claims. (Q1. 3109.6)

This invention relates to pickups for musical instruments, and moreparticularly, to piezoelectric pickup units for converting mechanicalvibrations generated in musical instruments into electrical signals thatmay be supplied to amplifiers and loudspeakers. Although certainfeatures of the invention may be applied in various musical instruments,it will be convenient to describe the invention in connection withelectric guitar apparatus. Having gained an understanding of this formof the invention, persons skilled in the art will appreciate the mannerin which the principles of the invention may be applied in otherinstruments.

Although the use of piezoelectric transducers in pickups for musicalinstruments has been suggested heretofore, the actual structuresproposed have been deficient in some respects. For example, difiicultieshave been experienced in establishing adequate electrical connectionsbetween the transducers and the lead wires for conducting the signals toan amplifier. Moreover, shielding has been a problem because the signalsare applied to high impedance circuits where stray radiation effects mayresult in the production of noise components of substantial magnitude.

It is a general object of this invention to provide improved pickups ofthe piezoelectric type which can be manufactured economically and whichwill give satisfactory service under the environmental conditionsencountered in the use of musical instruments. Other objects andadvantages of the invention wil become apparent as the descriptionproceeds.

A pickup in accordance with a preferred embodiment of the invention ismade up of a plurality of transducer units supported on a base orplatform unit. Each transducer unit includes a hollow, tunnel-shaped,piezoelectric body having inner and outer surfaces which are coated withconductive material to form the terminals of the transducer. The outerconductive coating normally is grounded, and the inner coating carriesthe electrical signal which is to be amplified and used in theproduction of music.

The connection to the inner signal-carrying terminal of each transduceris provided by a lead wire carried by a preformed shoe. The shoeconforms in shape to the inner surface of the transducer, and the leadwire passes through the shoe and has a splayed end which may be broughtinto contact with the inner terminal of the transducer when the shoe ispressed into place. A suitable non-conductive adhesive secures the shoeto the transducer body and serves to hold the lead wire in contact withthe inner terminal.

The platform unit of the assembly is provided with electricallyconductive coatings also. These coatings are so arranged as to provideelectrical connections with the coatings on the outer surfaces of thetransducer units when the parts are brought into their final positions.Means are provided for grounding the coatings on the platform unit andthe outer surfaces of the transducer units so as to shield the innerterminals and lead wires of the assembly against stray radiation.

A more complete understanding of the invention will be gained from aconsideration of the following detailed description of the embodimentillustrated in the accompanying drawings in which:

FIGURE 1 is a partial perspective view of an electric 3,154,701 PatentedOct. 27, 1964 guitar embodying pickup apparatus constructed inaccordance with the invention;

FIGURE 2 is a plan view of a bridge assembly for the guitar of FIGURE 1;and

FIGURE 3 is an enlarged cross-sectional view taken along the line 3-3 ofFIGURE 2.

The guitar illustrated in FIGURE 1 is of the classic type. It includes aguitar body 2 which may be of conventional construction. Strings 4 aremounted on the guitar in the usual manner, the means for securing thelower ends of the strings 4 being illustrated diagrammatically at 6 inFIGURE 1. The strings 4 are tensioned and, just forwardly of the means6, they pass over a bridge assembly designated generally by thereference numeral 8.

The bridge assembly 8 includes a plurality of piezoelectric transducerunits 10 supported by a platform or base unit 12 which is mounted on theinstrument body 2. When the strings 4 are vibrated, the transducer units10 are stressed so as to generate electrical signals correspond ing tothe vibrations of the strings 4. These signals are transmitted throughsuitable leads to cable means 14 connected to a conventional amplifierand loudspeaker system (not illustrated). The cable means 14 preferablyis a coaxial cable having an active signal-carrying core and a groundedconductor insulated from and disposed in surrounding relationship withrespect to the core.

Each of the transducer units It is adapted to cooperate with one of thestrings 4. To this end, the upper surface of each is provided with astring-receiving notch or groove 16 terminating at its forward end in anabrupt shoulder 18. When a string 4 is disposed within the groove 16 ofa transducer unit 10, the shoulder 18 serves to define the end of thevibrating length of that string.

Each of the transducer units 10 includes as its active component ahollow, tunnel-shaped, generally semi-cylindrical body 2 of materialcapable of generating electrical signals in response to pressurevariations. Polarized ceramic materials such as barium 'titanate havebeen found to be suitable for this purpose. The terminals for the unitare provided by coatings 22 and 24 of conductive material, such assilver, disposed respectively on the inner and outer surfaces of thebody 20. These coatings 22 and 24 are applied in such a way as to leavethe end faces 26 of the legs of the ceramic body 20 bare. Hence, thereis no electrical path from the interior coating 22 to the outer coating24.

After the coatings 22 and 24 have been applied to the ceramic body 20, athin preformed covering member or shoe 28 of fiber glass or othersuitable insulating material is brought into position and secured toboth the inner surface bearing coating 22 and to the end faces 26 of thelegs of the body 20'. A non-conducting cement or adhesive 30, such as anepoxy resin, is admirably suited for this purpose.

Prior to the attachment of shoe 28 to the transducer body 20, a leadwire or pigtail 32 is inserted through a small opening at the top of theshoe 28, and the upper end 34 of the lead wire 32 is splayed out overthe topmost portion of the shoe. The adhesive 30 normally is applied tothe coating 22 and to the end faces 26 of the legs of the ceramic body2. Then when the shoe 28 is pressed into place, the splayed end 34 ofthe lead wire 32 is brought into contact with the conductive coating 22to establish a good electrical connection. The splayed end 34 is heldsecurely by the adhesive 36) and by the shoe 28. This type of assemblyprovides assurance that the electrical connections will remain in goodcondition over long periods of active service.

The portions of the shoe 28 that underlie the legs of the ceramic body 2provide flat surfaces which enhance the positional stabilityof the unit.This feature is of considerable importance in some instances where themanufacturing operations involved in forming the ceramic bodies do notgive these bodies perfectly flat bearing faces and where, in the absenceof the shoes 28, rocking might result.

After a shoe 28 has been cemented in place, a transducer unit may becompleted by applying to the bottoms of the legs a conductive coating 36of a material such as silver. This coating is applied in such a way asto form a continuation of the coating 24 on the outer surface of theceramic body 20. It will be noted from FIGURE 3 that the coating 36 isinsulated from the coating 22 on the inner surface of the ceramic bodyby the fiber-glass shoe 28.

The platform or base unit 12 is formed of a body of plastic 13 providedwith a plurality of conical openings 38 in its upper surface, with theopenings 38 being so arranged that each of the transducer units 10 mayoverlie one of these openings. With this arrangement, the lead wire 32from a transducer unitlil may be passed down wardly through one of theopenings 38 for connection to the signal-carrying conductor in the cable14 leading from the pickup to an amplifier.

Referring to FIGURES 2 and 3, it will be observed that the transducerunits 10 need not be in exact alignment longitudinally of the base unit12. Thelead wires 32 normally are slack as they pass through theopenings 38, so that the transducer units 10 may be moved slightlyrelative to the platform unit 12 when the musician desires to make smalladjustments in the vibrating lengths of the strings 4 of the guitar.Such fine adjustments are of some importance to classic guitar artists.

The interior of the platform unit 12 is provided with a longitudinalgroove or channel 40 and with a transverse groove 42. The cable 14enters the longitudinal groove 40 at one end of the assembly, and thelead wires 32 from the transducer units 10 enter the groove 40 throughthe openings 38. The lateral groove'42 provides a channel for a groundwire 44 connected at one end to the ground conductor in the cable 14 andconnected at the other end to an electrically conductive coating 46 onthe exterior surface of the platform unit 12. An epoxy resin 48 may beemployed to fill the groove 42 after the lead 44 has been brought intoplace.

The coating 46 is applied to the plastic body 13 in such a Way as tocover all of the exposed surfaces except those located at the bottom ofthe base unit. Spraying techniques have been found suitable. If thecoating 46 is applied in such a way as to enter the openings 38 at thetop of the plastic body 13, these openings should be reamed or otherwisetreated to remove the electrically conductive material therefrom or tointerrupt all possible electrical paths between the walls of theseopenings and the coating 46. Then when the lead wires 32 are broughtdown through the openings 38 there is no danger that these lead wireswill be in electrical communication with the coating 46 on the exteriorsurface of the platform unit 12.

After the transducer units 10 and the cable 14 have been brought intoposition with respect to the platform unit 12 and the leads 32 have beenconnected together and to the core of the cable 14, the bottom surfaceof the platform unit 12 may be finished. The bottom of the plastic body13 has secured thereto by a suitable non-conductive cement 50 a sheet ofpaper or other non-conducting material 52. This provides a smooth bottomsurface for the assembly, and the bottom surface then may be coated witha polyester resin 54 for protecting the paper 52 and a conductivecoating 56 may be applied'over theentire bottom of the device.

The coatings 46 and 56 are in electrical contact with each other and thecoating 46 is in electrical contact with the coating 24 on the exteriorsurface of the transducer units 10. Since the coating 46 is groundedthrough the lead 44, it will be apparent that the assembly provideshighly efficient shielding for the electrical components within theinterior of the assembly. In this connection it will be observed alsothat the plastic body 13 which forms the base of the assembly isprovided with end walls 58 and 69 which extend upwardly to levels abovethe tops of the inner terminals of the transducer units. The coating 46covers these end walls also so as to provide protection against theentrance of radiation through the ends of the transducer units. Thearrangement is such that the grounded shielding means substantiallysurrounds the signal-carrying components, and there is very littlechance of stray radiationaifecting the electrical signals-appearing onthe internal terminals 22 of the transducer unit or on the lead wires 32that carry these signals to the'cable 14.

Although a single embodiment of the invention has been illustrated anddescribed in detail, various changes and modifications will suggestthemselves to persons skilledin the art. It is intended, therefore, thatthe foregoing description be considered as exemplary only and that thescope of the invention be ascertained from the following claims.

I claim: a

1. A pickup for converting mechanical vibrations in a musical instrumentinto electrical oscillations comprising a piezoelectric transducer ofgenerally semi-cylindrical shape having an inner surface and an outersurface and having electrically conductive material on said surfaces, athin shoe of electrically insulating material conforming in contour tothe inner surface of said transducer and being adhesively securedthereto, and a lead wire'passing through said shoe and having an endportion held in conducting relation with said electrically conductivematerial on said inner surface.

' 2. A pickup for converting mechanical vibrations in a musicalinstrument into electrical oscillations comprising a hollowpiezoelectric transducer body of generally semi-. cylindrical shapehaving a-pair of legs, said transducer body having an inner and an outersurface and electrically conductive coatings on said surfaces, a thinfiber glass shoe conforming in contour to said inner surface and to theend surfaces of said legs of said transducer body and being adhesivelysecured to said body, and a lead wire passing through said shoe andhaving an end portion held in-conducting relation with said electricallyconductive coating on said inner surface.

3. A pickup for converting-mechanical vibrations in a musical instrumentinto electrical oscillations comprising a support member having anelectrically conductive surface, a tunnel-shaped piezoelectrictransducer having at least two legs supported on said'conductive surfaceof said support member, said transducer having inner and outer surfacesand electrically conductive coatings on such surfaces, a thin shoe ofelectrically insulating material conforming in contour to said innersurface and to the end surfaces of said legs and being adhesivelysecured thereto, an electrically conductive coating on the exposedsurfaces of the portionsof said shoe at the ends of said legs, thelast-mentioned coating being in electrical contact with both the coatingon the outer surface of the transducer and said electrically conductivesurface of said support member, a lead wire passing through saidshoe andhaving an end portion held in conducting relation with said electricallyconductive coating on said inner surface, and means for grounding saidelectrically conductive surface of said support member.

4. A bridge for a string instrument comprising a base member having anelongated interior channel and a plurality of longitudinally spacedapart openings extending inwardly from the top of the base member tosaid channel, electrically conductive material on the bottom, side andtop surfaces of said base member, a plurality of tunnel-shapedpiezoelectric transducers overlying said openings and having legssupported 'by the top of said base member, electrically conductivematerial on the outer surface of each of said transducers in electricalcontact With said electrically conductive material on the surfaces ofsaid base member, electrically conductive material on the inner surfaceof each of said transducers, and a plurality of electrical leads eachbeing connected at one end to the conductive material on the innersurface of a transducer and passing downwardly through the openingtherebeneath into said channel in said base.

References Cited in the file of this patent

1. A PICKUP FOR CONVERTING MECHANICAL VIBRATIONS IN A MUSICAL INSTRUMENTINTO ELECTRICAL OSCILLATIONS COMPRISING A PIEZOELECTRIC TRANSDUCER OFGENERALLY SEMI-CYLINDRICAL SHAPE HAVING AN INNER SURFACE AND AN OUTERSURFACE AND HAVING ELECTRICALLY CONDUCTIVE MATERIAL ON SAID SURFACES, ATHIN SHOE OF ELECTRICALLY INSULATING MATERIAL CONFORMING IN CONTOUR TOTHE INNER SURFACE OF SAID TRANSDUCER AND BEING ADHESIVELY SECUREDTHERETO, AND A LEAD WIRE PASSING THROUGH SAID SHOE AND HAVING AN ENDPORTION HELD IN CONDUCTING RELATION WITH SAID ELECTRICALLY CONDUCTIVEMATERIAL ON SAID INNER SURFACE.